Conventionally, the dimensions of a display lens for a portable electronic device, such as a mobile phone, are driven by the desired viewable display area and the industrial design of the phone. Therefore, the display lens is not often thought of as an acoustic apparatus or speaker. More often than not it is because those skilled in the art have long recognized that a display lens often has a poor dynamic response due to its physical dimensions.
The configurations of conventional mobile phone display lens have mechanical modes that are very often plentiful and grouped together within the phone's audio band. Any designer of dynamic speakers desires to have as few of these mechanical modes as possible (with the exception of the piston mode) within the phone's audio band. In order to provide the smoothest frequency response of the display lens' driven surface, a designer would greatly like to have these mechanical modes as evenly spaced as possible. Often the front surface of a mobile phone has dimensions that are close to small integer ratios such as 3:2, 4:3, and 16:9, and in a worst case scenario 2:1. For example, one popular phone in the marketplace today has a display lens of about 50 mm×100 mm for a ratio of 2:1. These low-integer ratios result in mechanical modes that bunch up in certain areas of the audio band. FIG. 1 is an illustration of prior art glass lens modal distribution that shows where certain mechanical modes lie within a frequency domain.
In FIG. 1, each vertical line represents a mode at the frequency the line crosses the horizontal axis. There are fourteen modes within a 4 kHz phone audio band and some of these modes tend to group together due to the dimensional ratio of the display lens. At 1 kHz a laser vibrometer measured two modes only within a few Hz of each other after the display lens of a phone was driven mechanically.
Accordingly, there is a need to overcome this exemplary grouping of modes and resulting poor dynamic response of display lens when excited mechanically in order to produce an acoustic signal.